1. Field of the Invention
This invention relates to a method for producing a wear-detection probe For a brake lining material such as a brake pad for a disc brake in a vehicle or the like.
2. Statement of the Prior Art
For convenience of explanation, a conventional wear-detection probe for a brake lining material will be described below by referring to FIGS. 5 through 9.
FIG. 5 is a cross-sectional view of a conventional disc brake For a vehicle. FIG. 8 is a plan view of a conventional wear-detection probe for a brake lining material. FIG. 7 is a perspective view illustrating a conventional process for producing a conventional probe. FIG. 8 is a cross-sectional view illustrating the conventional process for producing the conventional probe. FIG. 9 is a perspective view illustrating the conventional process for producing the conventional probe.
As shown in FIG. 5, a disc brake 1 for a vehicle generates a braking force when a pair of brake pads 3 or the like are pressed against the two sides of a rotor 2 which rotates under rotation of a wheel. In this disc brake 1, a probe 10 juxtaposed with the brake pad 3 detects the residual thickness of the pad 3 worn by contact with the rotor 2, so that a warning signal can be generated before the brake pads become overworn.
The wear-detection probe 10, as shown in FIG. 8, is made by mold-forming a resin material 12 around a U-turned portion 11a which is formed by bending a linear conductor such as an insulated electrical wire 11 or the like in a U-shape. The probe 10 is secured to the rear metal 3a of the brake pad 3 at a flange 10b so that the top end 10a of the probe 10 is directed to the rotor 2 and both ends of the insulated electrical wire 11 are drawn out of the probe 10 so as to be connected to an alarm circuit (not shown). The brake pad 3 is worn due to contact with the rotor 2 every time the brake is operated, and the top end 10a of the probe 10 is also worn with reduction of the residual thickness of the brake pad 3. Consequently, the U-turned portion 11a is gradually worn. When the residual thickness of the brake pad reaches a predetermined value, the U-turned portion 11a is cut off. The alarm circuit detects the disconnection of the U-turned portion and generates a warning signal.
In the probe 10, since a wear limit of the residual brake pad 3 is detected by the disconnection of the U-turned portion 11a, it is necessary to accurately position the U-turned portion 11a in the resin material 12, in particular, in a wear-progressing direction A (see FIG. 6) with respect to the residual thickness of the brake pad 3.
Accordingly, in a conventional method of producing the probe 10, as shown in FIG. 7, first, the insulated electrical wire 11 is disposed around a positioning pin 20 mounted in a metal mold member 30 to form the U-turned portion 11a, second, a metal mold comprising the metal mold member 30 and the other metal mold members (not shown) closes a space around the U-turned portion 11a of the insulated electrical wire 11 while holding the wire 11 by the pin 20 so that the wire does not shift in the mold, and third, a molten resin material is poured into the closed space and solidified in the mold. Thus, the insulated electrical wire 11 is correctly positioned in the molded resin material 12.
However, in the conventional method for producing the conventional wear-detection probe, after molding the probe a pin drawn-out hole 21 is left inside the U-turned portion 11a in a probe member 10P as shown in FIG. 8, since the positioning pin 20 is drawn out together with a molded article (probe member) upon removing the molded article from the metal mold. If the probe member 10P with the pin drawn-out hole 21 is used for the probe 10, the probe 10 is reduced in strength. Consequently, when a pushing force F (FIG. 6) caused by contact with the rotor 2 is applied to the top end 10a of the probe 10, the probe is easily broken. Further, the U-turned portion 11a is deflected into the hole 21, thereby displacing the disconnection position of the U-turned portion 11a, since the hole 21 is left inside the U-turned portion 11a.
Commonly, heretofore, as shown in FIG. 9, a packing material 22 or the like is filled in and secured to the pin drawn-out hole 21 by an adhesive to increase the strength of the probe 10, thereby preventing the U-turned portion 11a from being deflected into the hole. However, this increases the steps necessary for producing the probe including additional steps of inserting the packing material 22 into the hole 21 and applying the adhesive. Further, it is necessary to leave the probe 10 in the mold until the adhesive is hardened, thereby increasing a producing period in time.